Solid materials for use as an element between the electrodes of a battery, an electric double-layer capacitor (electric double-layer condenser), or the like, have been developed wherein the use of a structural material which prevents a short-circuit between the electrodes is unnecessary and wherein it is unnecessary to be concerned about the leakage of electrolytic solution. It is required that materials used for these have both the following two properties: a high ion conductivity as an ion conductor and structural stability and processability as a separator on a higher level. As examples of such materials, an intrinsic polymer electrolyte (one that is completely solid) and a polymer gel electrolyte are known.
However, since the ion conductivity of intrinsic polymer electrolytes is basically low (less than 10−4 S/cm at room temperature), an intrinsic polymer electrolyte used at room temperature has not yet reached practical use.
On the other hand, as examples of polymer gel electrolytes, a homogeneous gel electrolyte made by swelling an organic polymer (polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, etc.) with an electrolytic solution made by dissolving a supporting electrolyte (LiClO4, quaternary ammonium salts, etc.) in a polar solvent (for example, see patent documents 1 and 2); a structure-based gel electrolyte made by forming an organic polymer (polyolefin, polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, etc.) into a porous body and by maintaining an electrolytic solution in micropores of the porous body (for example, see patent documents 3 and 4); and that made by impregnating a network-structure support medium comprising a non-electroconductive polymer with an electrolyte (for example, see patent document 5) can be mentioned.
The homogeneous gel electrolyte has the advantage that the electrolytic solution rarely leaks, but it has disadvantage that the ion conductivity is low and does not reach the ion conductivity of an electrolytic solution itself because the maximum capacity to maintain the electrolytic solution is about five times as large as that of organic polymers. On the other hand, the structure-based gel electrolyte has a problem in that the electrolytic solution is likely to leak. Also, both of these have the problem that the kind of solvent used in the electrolytic solution is restricted according to a kind of organic polymer used in terms of compatibility between the organic polymer used as a support maintaining the electrolytic solution and the solvent. For these reasons, the development of ion conductors which have a high capacity to maintain all electrolytic solutions and in which leakage of the electrolytic solution rarely occurs has been anticipated.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2001-351832
Patent Document 2: Japanese Unexamined Patent Application, Publication No. H11-149825
Patent Document 3: PCT International Publication No. WO 95/06332
Patent Document 4: PCT International Publication No. WO 95/15589
Patent Document 5: Japanese Unexamined Patent Application, Publication No. 2000-11758